1. Field of the Invention
The present invention relates to a grease gun, and more particularly to an oil flow control structure for grease gun that regulates outlet pressure according to user demands.
2. Description of the Related Art
As shown in FIG. 8 and FIG. 9, a structure of grease gun having dual-pumping rods is disclosed. A high pressure passage 21B and a low pressure passage 22B are disposed in a main body 1B. A first pumping rod 31B and a second pumping rod 32B are respectively disposed in the high pressure passage 21B and the second pressure passage 22B. The first pumping rod 31B and the second pumping 32B can perform piston motions along an axis of the rod to push grease within the high pressure passage 21B and the low pressure passage 22B. In addition, a drainage portion 9 is disposed between the low pressure passage 22B and the inflow end 11B. The drainage portion 9 comprises a split-flow hole 91 and a slot way 92 circularly disposed, thereby communicating with the low pressure passage 22B. A normal close valve 93 is disposed to the split-flow hole 91 to prevent the low pressure passage 22B from communicating with the slot way 92. When counter-acting force received by the second pumping rod 32B performing piston motion that outwardly pushes grease exceeds a predetermined value, the normal close valve 93 is pushed by the pressure of grease to conduct the low pressure passage 22B and the slot way 92 such that grease within the low pressure passage 22B is pushed by the second pumping rod 32B to return to a grease barrel 8, and only grease within the high pressure passage 21B can be pushed out.
The foregoing design can use two passages with different cross-sectional areas to generate oil injection pressures having different high low pressure. However, it may need enormous components. The processing procedure is also complicated during the production process to cause difficult production and extremely high cost.